Display device and manufacturing method for the same

ABSTRACT

In a manufacturing method in which a source line is provided around a pixel electrode provided on a substrate, an insulating film having open regions that will provide a source and a gate is formed, the source and the drain are formed, and a semiconductor film and a gate are provided on the source and drain, the above constituents are formed substantially under atmospheric pressure. Since manufacture can be accomplished substantially under the atmospheric pressure, no special apparatus, such as a vacuum chamber, is required, permitting a display device to be manufactured at lower cost.

TECHNICAL FIELD

The present invention relates to a display device and a manufacturingmethod therefor and, more particularly, to a device for performingdesired display by using an electrophoretic ink, and a manufacturingmethod therefor.

BACKGROUND ART

Display devices driven by semiconductor elements have been manufacturedby utilizing advanced equipment, such as a high vacuum apparatus.

However, utilizing such advanced equipment poses a problem of highmanufacturing cost for the display devices driven by the semiconductorelements.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a display device thatcan be manufactured at lower cost, and a manufacturing method for thesame.

A display device in accordance with the present invention includes apixel electrode and a transistor for applying a voltage to the pixelelectrode,

wherein at least an active layer of the transistor is formed of anorganic material.

Furthermore, a manufacturing method for the display device in accordancewith the present invention includes a step for providing a source linearound a pixel electrode provided on a substrate, a step for forming aninsulating film pattern having an opening of a region for a source and adrain, a step for forming the source and the drain, a step for providinga semiconductor film on the source and the drain, and a step forproviding a gate on the semiconductor film, the respective steps beingimplemented substantially under atmospheric pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing an embodiment of a display device inaccordance with the present invention.

FIG. 2 is a diagram showing a state wherein an electrophoretic ink hasbeen applied.

FIG. 3 is a diagram illustrating a displaying principle of the displaydevice using the electrophoretic ink.

FIG. 4 is a process diagram illustrating a manufacturing method for adisplay device having the sectional structure shown in FIG. 1.

FIG. 5 is another process diagram illustrating the manufacturing methodfor the display device having the sectional structure shown in FIG. 1.

FIG. 6 is yet another process diagram illustrating the manufacturingmethod for the display device having the sectional structure shown inFIG. 1.

FIG. 7 is still another process diagram illustrating the manufacturingmethod for the display device having the sectional structure shown inFIG. 1.

FIG. 8 is a diagram illustrating the sectional structure taken along theline A—A shown in FIG. 7.

FIG. 9 is a diagram illustrating a method for exposing an externalterminal in the display device using the electrophoretic ink.

PREFERRED EMBODIMENTS OF THE INVENTION

A display device in accordance with the present invention that includesa pixel electrode and a transistor for applying a voltage to the pixelelectrode is characterized in that at least an active layer of thetransistor is formed of an organic material.

A preferred embodiment of the display device may be provided with a filmfor protecting a gate of the transistor and an electrophoretic ink layerprovided on the provided film and the pixel electrode. This arrangementpermits the manufacture to be implemented substantially underatmospheric pressure; therefore, no special apparatus, such as a vacuumchamber, is required, making it possible to manufacture the displaydevice at lower cost.

A manufacturing method for a display device in accordance with thepresent invention includes a step for providing a source line around apixel electrode provided on a substrate, a step for forming aninsulating film pattern having an opening of a region for a source and adrain, a step for forming the source and the drain, a step for providinga semiconductor film on the source and the drain, and a step forproviding a gate on the semiconductor film, and the manufacturing methodis characterized in that the respective steps are implementedsubstantially under atmospheric pressure. Since manufacturesubstantially under atmospheric pressure is possible, no specialapparatus, such as a vacuum chamber, is required, enabling a displaydevice to be manufactured at lower cost.

In a preferred embodiment, a step for electrolytically plating thesource line may be added to the aforesaid manufacturing method.Performing the electrolytic plating makes it possible to prevent staticelectricity.

Furthermore, in a preferred embodiment, a step for providing a film forprotecting the gate and a step for applying electrophoretic ink afterproviding the film may be added to the aforesaid manufacturing method.Providing the film allows a transistor portion to be protected. In thestep for providing the film for protecting the gate, the film isprovided by lamination.

Using a resin film with the pixel electrode for the substrate makes itpossible to implement a flexible display device.

According to the present invention, as another manufacturing method fora display device, there is provided a manufacturing method for a displaydevice having a terminal for receiving an external signal, including astep for providing a protective film on the surface of the terminal, astep for forming a display region in a state wherein the protective filmhas been provided, and a step for removing the protective film, thesurface of the terminal being exposed.

Preferably, the protective film is a seal attached to the terminal andremoved by peeling the seal, or the protective film is an insulatingfilm and the insulating film provided on the terminal is removed bylaser irradiation, or the protective film is a seal attached to theterminal and the seal is heated to produce a gas, which causes the sealto be removed by peeling. Adopting these exposing methods allows theterminal to be easily exposed.

Referring now to the accompanying drawings, an embodiment of the presentinvention will be described more specifically. In the drawings to bereferred to in the following description, the components similar tothose in other drawings will be denoted by the same reference numerals.The descriptions will be given in the following order: (1) the sectionalstructure of an organic TFT display device, (2) a manufacturing methodfor the organic TFT display device, and (3) a method for exposing anexternal terminal.

(1) Sectional Structure of an Organic TFT Display Device

FIG. 1 is a sectional view showing an embodiment of the display devicein accordance with the present invention. As shown in the drawing, thedisplay device according to the embodiment has a pixel electrode 101 anda source line 102 formed of ITO or the like, an insulating film 103, asource 104 a and a drain 104 b, a semiconductor layer 5, an insulatingfilm 6, and a gate 105 that are deposited on a substrate 1 in the orderin which they are listed.

In the present invention, a protective film 106 is provided to protectthe transistor portion, including the gate 105. The protective film 106is a lattice type film provided with an opening 107 in a portion thatcorresponds to the pixel electrode 101. By attaching the film 106, thetransistor portion can be protected. Furthermore, applyingelectrophoretic ink onto the film 106 also causes the electrophoreticink to enter the opening 107.

The electrophoretic ink may be directly disposed at the opening 107. Inthis embodiment, however, the electrophoretic ink is sealed in amicrocapsule. A liquid containing the microcapsule and a binder isapplied. FIG. 2 shows a state wherein the electrophoretic ink has beenapplied. As shown in the drawing, the electrophoretic ink is sealed in amicrocapsule 33, and the microcapsule 33 is disposed also at the opening107. An electrode, which is not shown, is further formed, and a voltageis applied to the microcapsule 33 by the electrode and the pixelelectrode 101. The application of the voltage electrically polarizes theelectrophoretic ink in the microcapsule 33, permitting desired displayto be performed, as will be discussed hereinafter.

Since the protective film 106 is a lattice type film, the lattice may beseen by an observer during display; however, this will not pose aproblem because the pixel is larger (the opening 107 is larger) in adisplay device or the like having a large screen. The protective film106 may be attached by laminating. Providing the lattice type protectivefilm 106 makes it possible to prevent short-circuiting of a gateelectrode portion or other wiring, and also to improve image quality,leading to improved reliability of a TFT.

In such a configuration, a voltage applied to the gate 105 causes achannel to be formed in the semiconductor layer 5, turning thetransistor ON. This brings the source 104 a and the drain 104 b intoconduction, and a predetermined voltage is applied between the pixelelectrode 101 and a transparent electrode, which is not shown. Theapplication of the voltage electrically polarizes the electrophoreticink in the opening 107, thus performing desired display.

The electrically polarized condition will be described with reference toFIG. 3. The drawing illustrates an electrically polarized condition of asingle microcapsule. In (a) of the drawing, an electrophoretic ink 50 inthe microcapsule exists between an electrode 34 and a transparentelectrode 32. The electrophoretic ink 50 is constituted by a liquidphase dispersion medium 61 and electrophoretic particles 51 dispersed inthe liquid phase dispersion medium 61. The pigmentation of the liquidphase dispersion medium 61 and that of the electrophoretic particles 51are to be of different colors.

Voltage sources 9 a and 9 b for applying voltages in opposite directionsfrom each other are connected through the intermediary of a switch 8.More specifically, the electrode 32 is connected to one end of each ofthe voltage sources 9 a and 9 b, while the electrode 34 is connected tothe other end of each of the voltage sources 9 a and 9 b through theintermediary of the switch 8. With this connection, the direction of avoltage to be applied can be changed by switching the switch 8. Bychanging the direction of the voltage to be applied, the electrophoreticdispersion liquid can be polarized so as to perform desired display.

More specifically, as shown in (b) of the drawing, by applying a voltagefrom the voltage source 9 a, the electrophoretic particles 5 can becollected at the transparent electrode 32, which is closer to anobserver. Under this condition, the observer sees the color of theelectrophoretic particles 51. On the other hand, as shown in (c) of thedrawing, by applying a voltage from the voltage source 9 b, theelectrophoretic particles 51 can be collected at the electrode 34, whichis farther from the observer. Under this condition, the observer seesthe color of the liquid phase dispersion medium 61.

Thus, by electrically polarizing the electrophoretic ink 50 in themicrocapsules, two types of colors that correspond to the directions inwhich a voltage is applied can be displayed. Hence, desired display canbe accomplished at each pixel, so that applying the configuration shownin FIG. 1 to all pixels permits a display device to be realized.Moreover, using a flexible material for the substrate 1 makes itpossible to implement a flexible display device.

(2) Manufacturing Method for the Organic TFT Display Device

The manufacturing method for the display device having the sectionalstructure shown in FIG. 1 will be described with reference to FIG. 4through FIG. 7.

First, as shown in FIG. 4, a source line 102 formed of ITO or the likeis provided around the pixel electrode 101 formed of ITO or the likeprovided on the substrate. The line width of the source line 102 is, forexample, 20 μm. As the material for the substrate, PET (polyethyleneterephthalate), for example, is used. The area indicated by a dottedline H in the drawing corresponds to one pixel.

The pixel electrode 101 may be formed on the substrate, or a substratewith the pixel electrode already formed thereon may be purchased andused. The source line 102 may be provided with electrolytic plating.This makes it possible to reduce wire resistance and improve operatingspeed. The plating can be also expected to function as a countermeasurefor static electricity.

Next, as shown in FIG. 5, an insulating film is formed, that has regions103 a and 103 b opened, which will provide a source and a drain,respectively. For the insulating film, polyimide (hereinafter referredto as “PI”), for example, is used.

Further, as shown in FIG. 6, the source 104 a and the drain 104 b areformed in the opened regions 103 a and 103 b. The source 104 a and thedrain 104 b may use palladium as their material. In this embodiment, thesource and drain are formed by injecting an electrically conductiveliquid into the regions 103 a and 103 b. For this formation, an ink jetmethod may be used. As the electrically conductive liquid, a solutioncontaining, for example, polyethylene dioxythiophene (hereinafterreferred to as “PEDOT”) dissolved in a solvent is used.

And, as shown in FIG. 7, a semiconductor film and an insulating film areformed in this order on the source 104 a and the drain 104 b. Lastly,the gate 105 is formed on the insulating film. The semiconductor film isformed using, for example, pentacene. For the insulating film, siliconoxide (SiO₂) is used. The gate 105 uses nickel, for example, as itsmaterial, and is formed by the ion beam sputtering method.Alternatively, the photolithography may be used for the formation. Thegate 105 may be formed also by using the ink jet method. In this case,an electrically conductive liquid, such as PEDOT, may be used. The linewidth of the gate 105 is, for example, 50 μm.

In the state shown in FIG. 7, as described above with reference to FIG.1, the lattice type protective film 106 having the opening 107 in theportion corresponding to the pixel electrode 101 is attached. And, theelectrophoretic ink is applied onto the attached protective film 106, asdescribed above with reference to FIG. 2. An electrode, which is notshown, is further provided on the applied electrophoretic ink. Then, byapplying a voltage, as described above, between the electrode, which isnot shown, and the pixel electrode 101, desired display can beperformed.

Manufacturing the organic TFT display device according to the foregoingprocess allows all steps to be implemented under atmospheric pressure byusing the ink jet method or the like. Hence, no special apparatus, suchas a vacuum chamber, is required, permitting the manufacture to beaccomplished at lower cost. The range of “substantially underatmospheric pressure” according to the present invention includes “in aliquid” and “a clean room”.

FIG. 8 schematically shows the sectional structure of a portion taken atthe line A—A in FIG. 7. As shown in the drawing, the section A—Aincludes a substrate 1, an insulating film 2 made of PI or the likeformed on the substrate 1, a source line 102, a source 104 a, the pixelelectrode 101, and the drain 104 b, which are formed in the same layeras the insulating film 2, the semiconductor layer 5, the insulatinglayer 6, the gate 105, and the protective film 106 covering the gate105. The portion above the pixel electrode 101 is not covered by theprotective film 106, and this portion provides the aforesaid opening107. Here, the thicknesses of the source 104 a and the drain 104 b are60 nm, and the distance between the source 104 a and the drain 104 b is,for example, 100 to 200 μm. The thickness of the semiconductor layer 5is, for example, 60 nm, the thickness of the insulating film 6 is, forexample, 1 μm, and the thickness of the gate 105 is, for example, 45 nm.

(3) Method for Exposing an External Terminal

In the display device manufactured according to the aforesaid process,the electrophoretic ink is applied by the ink jet method or the like;therefore, it is necessary to provide beforehand a terminal forreceiving signals to be displayed from the outside and to expose theterminal. To expose such a terminal, a protective film is provided inadvance on a terminal portion, and a display region or the like isformed with the protective film provided. After the display region orthe like is formed, the protective film is removed to expose the surfaceof the terminal.

In short, according to the manufacturing method for the organic TFTdisplay device having the terminal for receiving external signals, thesurface of the terminal is provided with the protective film, thedisplay region is formed with the protective film provided, then theprotective film is removed to expose the surface of the terminal.

For instance, as shown in FIG. 9, the surface of a display device 100 isprovided with a plurality of terminals T extending from a display region90, which is also provided on the surface. Hence, before applying theelectrophoretic ink, the terminals T are covered with a protective filmS, and the protective film S is peeled off after the electrophoretic inkis applied.

For the protective film, a protective sheet (so-called “seal”), forexample, may be used. In other words, the terminals are masked byattaching the sheet, then the sheet is peeled off after the displayregion or the like is formed. In this case, as the protective sheet,Revalpha (trade name), which is a thermal release sheet manufactured byNitto Denko Corporation, for example, is used. This thermal releasesheet is formed of a polyester base material with a thermal releaseadhesive agent applied to the base material. The sheet loses itsadhesive force and peels when heat of about 90° C. is applied to thesheet after it is attached.

Alternatively, an insulating film may be formed on the terminal Tportion, and the insulating film may be removed by laser irradiation orthe like later.

Adopting the aforesaid exposing method allows the terminals to be easilyexposed without using the photolithography technology. It is obviousthat the method for exposing the external terminals explained above canbe applied not only to electrophoretic ink, but also extensively to themanufacturing methods for display devices that include a step forapplying a liquid.

As described above, according to the present invention, by adopting theaforesaid sectional structure, by manufacturing according to theaforesaid method, and by exposing the external terminals according tothe aforesaid method, all manufacturing process steps can be implementedsubstantially under atmospheric pressure without using any specialapparatus, such as a vacuum chamber, thus providing an advantage in thatorganic TFT display devices can be manufactured at lower cost.

What is claimed is:
 1. A display device comprising: a pixel electrode; atransistor conductively connected to the pixel electrode, the transistorincluding: a first opening region, a drain of the transistor beingformed therein; a second opening region, a source of the transistorbeing formed therein, and a semiconductor film formed over the drain;and the source, wherein the first and the second opening region areseparated by an insulating material, and the drain and the source aremade from liquid material with conductivity.
 2. A display deviceaccording to claim 1, wherein the transistor further comprises aninsulating layer formed over the semiconductor film and a gate electrodeformed ever the insulating layer.
 3. A display device according to claim1, wherein at least one of the drain and the source includes a materialselected from the group consisting of palladium and PEDOT.
 4. A displaydevice according to claim 1, wherein the semiconductor film includespentacene.
 5. A display device according to claim 1, further comprisinga semiconductor layer over the pixel electrode and conductivelyconnected to the pixel electrode.
 6. A display device according to claim5, further comprising a protecting layer over the transistor, theprotecting layer including a recess corresponding to the pixelelectrode.
 7. A display device according to claim 6, wherein thesemiconductor layer is arranged in the recess.
 8. A display deviceaccording to claim 5, wherein the semiconductor layer includes anelectrophoretic material.
 9. A display device according to claim 8,wherein the electrophoric material further comprises a plurality ofmicrocapsules.